Separate the mushroom caps from the stems. Chop the stems and reserve them for later use.
In a large skillet, heat the butter and the oil over medium heat until the butter melts.
Add the mushroom caps to the pan and sauté them until they begin to turn brown, for about 5 to 8 minutes. Transfer the caps to a plate.
Add the chopped mushroom stems, garlic, and fresh parsley to the hot pan and sauté them for 5 minutes.
Add the browned mushroom caps back into the pan, cover, and cook over low heat for 10 to 15 minutes, until all the mushrooms are cooked through and tender.